Google is very secure in it's position. Plus, MANY people have some very good reasons not to abandon it. There is their
PR ranking system, Google Ad Sense, Google Docs, Gmail, etc, all which will help them from being dislodged in the market. They are not search engines, but it gives them a huge amount of power on the internet. Bing would need to contribute something at least as major in order to knock Google back. Plus, people just don't love Microsoft and its products the same way anymore. Google has the brand image.